The present invention relates to a detection system for receiving incoming signals coming from many different directions and presenting indications of the direction and/or range of a source of incoming signals. More particularly, it relates to a detection system which comprises (i) means for receiving incoming signals in a manner that the Doppler effect is produced to vary the carrier frequency of the incoming signals (ii) a matched filter coupled to the receiving means to pulse-compress output signals therefrom, and (iii) an indicator for displaying output signals from the matched filter, and which forms a plurality of reception beams successively in angular directions. This type of detection system is enclosed in U.S. Pat. No. 4,425,634.
Hereinafter, the invention will be described as embodied in a scanning sonar for receiving incoming signals from many different directions in a wide range of angles to indicate the direction and range of objects on the face of an indicator.
Referring to FIG. 12 in which a relevant portion of a prior art detection system is shown, one hundred and twenty ultrasonic transducers 1CH through 120CH are disposed on an imaginary circle as equidistantly spaced, which forms one row of transducers Preamplifiers P1 through P120 amplify reception signals caught by the ultrasonic transducers 1CH through 120CH respectively. A selector SW successively connects, at a predetermined speed, the output terminal of each of the preamplifiers P1 through P120 to the input terminal of a beamformer BM to supply the beamformer with the output signals of each of the preamplifiers P1 through P120. As a result the Doppler effect is produced to vary the carrier frequency of the incoming signals received The beamformer comprising a matched filter pulse-compresses the received signals to produce signals having come in a desired direction and detected The reception signals produced by each of the transducers 1CH through 120CH are selected and derived at the output terminals of the preamplifiers P1 through P120 to be supplied to the input terminal of the beamformer.
With the prior art detection system, six rows of ultrasonic transducers are disposed in parallel with each other on the surface of a cylinder along the circumference thereof, with each row comprising one hundred and twenty ultrasonic transducers. Thus, seven hundred and twenty ultrasonic transducers are disposed on the surface of a cylinder, and the same number of preamplifiers are required to be incorporated in the receiving unit of the detection system, since all the ultrasonic transducers are separately and respectively connected to the corresponding preamplifiers. The switch SW is incorporated between the output terminals of the preamplifiers P1 through P120 and the input terminal of the beamformer, and the reception signals produced by each of the transducers 1CH through 120CH are selected by the switch SW to be applied at the input terminal of the beamformer BM. Accordingly, the dimensions of the receiving unit and the electric power consumed by the receiving unit are determined by the number of the preamplifiers. Manufacturing cost of the receiving unit is substantially determined by the cost of the preamplifiers.